Start by making the barrel. Cut an 18″ length of CPVC.
Wear safety goggles or a face shield when cutting CPVC, because flecks of the material are sharp and can get in your eyes. The friction from your saw can also break down the polyvinyl chloride, releasing toxic fumes—flip to Chapter 11, the Electro-Didgeridoo, for more info on the dangers of heating PVC and its relatives.
Use your finger to clear away all the burrs and sharp edges from the ends, as these will ultimately tear up the marshmallows and annoy you.
Measure 3/4″ from one end and mark it, as shown in Figure 24-4. This end of the barrel is the breech, where the explosion happens. The other end is the muzzle, where the marshmallow flies out.